Biochemical and Morphological Comparison of Postsynaptic Densities Prepared from Rat, Hamster, and Monkey Brains by Phase Partitioning

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Abstract
A new procedure for the preparation of postsynaptic densities (PSD) is described. A synaptic membrane fraction was homogenized in an aqueous 2-phase polymer system containing Poly(ethylene glycol) 6000 (5% wt/wt) and Dextran T500 (6% wt/wt) containing 1% 1-o-n-octyl-.beta.-D-glucoside. Following a brief centrifugation to separate the phases, highly purified PSD banded at the interface of the 2 phases. Using this procedure PSD were isolated from rat and hamster cerebral cortex and from the frontal cortex, cerebral cortex, hippocampus and pooled caudate/putamen regions of M. mulatta Rhesus monkeys. The isolated PSD appeared as curved bars when sectioned or as discs when viewed en face in the EM. The hamster PSD were associated with large numbers of small rod-like structures 4.5 nm thick and 28 nm long. Similar structures were present, although in fewer numbers, in the rat and monkey preparations. Polyacrylamide gel electrophoresis showed that the PSD a complex population of proteins with major components having MW of 180,000, 130,000, 110,000, 94,000, 65,000, 60,000 and 51,000. Reaction of polyacrylamide gels with 125I-concanavalin A (Con A) identified 2 major (apparent MW 180,000 and 130,000) and 3 minor (apparent MW 230,000, 145,000 and 110,000) Con A-binding glycoproteins in the PSD fractions. Although some quantitative variation between species and brain regions was apparent, the overall protein and glycoprotein composition was similar for all fractions studied.